A Method for Improving Stability of Grid-Connected Inverters Based on the Q-Axis Voltage Feedforward Control

In the weak grid condition, a high-bandwidth phase-locked loop (PLL) increases the frequency range of the negative incremental resistor behavior of the inverter's q-q channel impedance, which results in the decrease of the system stability. Though reducing the PLL bandwidth can improve the stability of the system, this will adversely affect the system dynamic response speed. To address this issue, a method based on the q-axis voltage feedforward control is proposed. This method compensates the phase of the q-q channel impedance of the inverter in the low frequency band without changing its amplitude. More specifically, a new controller is employed in this method, which can effectively eliminate the negative effect of the PLL. The performance of the proposed method is verified through the simulations and is compared to the proportional controller-based control method.